MEES Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/19655
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Item BIRD COMMUNITY RESPONSE TO CONSERVATION RESERVE PROGRAM HABITAT IN MARYLAND(2010) Blank, Peter Joshua; Dively, Galen P.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The populations of many bird species in the United States that use early-successional habitats have been substantially declining over the last 40 years. The main reason for these declines is habitat loss. Land enrolled in the U.S. Department of Agriculture's Conservation Reserve Program (CRP) often represents the only uncultivated herbaceous areas on farmland in the mid-Atlantic and therefore may be important habitat for early-successional bird species. CRP filter strips are strips of herbaceous vegetation that are planted along agricultural field margins and are usually planted with native warm-season grasses or introduced cool-season grasses. We studied the breeding and wintering bird use of CRP filter strips adjacent to wooded edges in Maryland from 2004-2007. We conducted bird and vegetation surveys in filter strips and measured landscape attributes around CRP plantings. We used 5 bird community metrics (total bird density, species richness, scrub-shrub bird density, grassland bird density, and total avian conservation value), species-specific densities and abundances, nest densities, and nest survival estimates to assess the habitat value of filter strips for birds. Bird community metrics were greater in filter strips than in field margins without filter strips, but did not differ between cool-season and warm-season grass filter strips. Most breeding bird community metrics were negatively related to the percent cover of orchardgrass (Dactylis glomerata). Several grassland birds were more common in wide filter strips (>60 m) compared to narrower filter strips (<30 m). The density of early-successional bird species was greater in filter strips with higher plant species richness and shorter and less dense grasses. Wintering bird use was significantly less in filter strips mowed in the fall than in unmowed filter strips. The abundance of northern bobwhite (Colinus virginianus), an important game bird and species of conservation concern, was positively associated with the percent cover of CRP land in the surrounding landscape. These results suggest that the CRP has created additional habitat for many early-successional bird species, but changes in the planning and management of CRP plantings may improve their habitat value for breeding and wintering birds.Item Investigating the role of the Mid-Atlantic inner continental shelf as a marine finfish nursery: a comparative approach(2010) Woodland, Ryan Jordan; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The paradigm of estuarine-dependence in marine fishes has been challenged by evidence of facultative recruitment by juveniles to both estuarine and inner continental shelf (ICS) nursery habitats. This ecological flexibility suggests that the potential nursery area for marine fishes may be more expansive than previously considered. Two lines of investigation were undertaken to evaluate the overarching hypothesis that ICS habitats serve a nursery function for finfish that also use estuarine nurseries: 1) a direct comparison of seasonal, annual and compositional assemblage structure between an ICS habitat of the Middle Atlantic Bight (Delmarva Peninsula) and an adjacent estuary (lower Chesapeake Bay); and 2) an investigation of trophic structuring within an ICS demersal finfish assemblage with an emphasis on ontogenetic niche. In comparisons between nursery types, there was a strong seasonal similarity in assemblage structure between the estuary and ICS despite significant differences in abundance estimates at the species level. Juvenile trophic niche of two indicator species, bluefish and bay anchovy, was wider and more diverse in the estuary yet physiological condition was similar or higher in the ICS. In focused studies on the ICS food web, diet overlap was common among consumers, yet stable isotope evidence indicated prey resources were partitioned along vertical (trophic position) and horizontal (pelagic-benthic pathway) trophic axes. Benthic and pelagic food webs were tightly coupled in most juvenile phase finfish; yet, this relationship showed signs of decoupling in older age classes, suggesting an increased reliance on benthic trophic pathways with age and size. Several prey species that link pelagic and benthic food webs were shown to be important in the diets of demersal finfish, particularly mysid shrimp. Comparative assemblage and food web studies demonstrated that the ICS functions as summer nursery habitat for a wide variety of temperate marine finfish that also use proximal estuarine nurseries. The contribution of ICS nurseries to annual juvenile production represents a critical, but unknown component of population demographics for many marine species and must be considered to conserve essential fish habitats and account for recruitment variability in fisheries stock assessments.Item Stable nitrogen isotopes (&delta15N) in the eastern oyster (Crassostrea virginica) as an indicator of nitrogen source(2010) Fertig, Benjamin Meir; Dennison, William C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation demonstrates that stable nitrogen isotope signatures (δ15N) in oysters (Crassostrea virginica) can identify anthropogenic nitrogen sources (a cause of degraded water quality) at multiple spatial scales in Chesapeake Bay and Maryland's Coastal Bays. Fieldwork, monitoring and land use data, spatial analyses, and modeling techniques were employed. Due to minimal tissue &delta15N variations between individuals as replicates (standard error < 0.5 /), a sample size of five individuals optimally balanced error with effort. Transplantation verified convergence of oyster &delta15N after changes in nitrogen source while modeling quantified temporal integration (four months for muscle, two to three months for gill and mantle) and measurements over two years demonstrated seasonal &delta15N increases in seston (summer) and oysters (winter). At the small scale (10s of km2), oyster tissues in Monie Bay's creeks (varying by watershed land use) were dominated by anthropogenic nitrogen transported to Monie Bay from Wicomico River whose watershed inputs were predominantly manures (6.8 x 104 to 2.4 x 106 kg N yr-1), not sewage (2.0 x 105 kg N yr-1) or septic (1.1 x 105 kg N yr-1). This has large implications for Delmarva Peninsula: home to 4,630 poultry feeding houses (generating 3.9 x 106 to 1.3 x 108 kg N yr-1) and 1.2 x 106 people (combined sewage and septic generating 3.7 x 106 kg N yr-1), thus a poultry:human nitrogen generation ratio of 1:1 to 91:1. At the medium spatial scale (100s of km2), water quality in Maryland's Coastal Bays was susceptible to runoff. Macroalgae &delta15N (Gracilaria sp.) responded rapidly (4 days) over 100s of km2, while oyster &delta15N responded slowly (2 months) over 10s of km2. Broadly, in Chesapeake Bay (large scale, 10,000s of km2), oyster &delta15N was correlated to land use, stream and tributary water quality, and it reflected tributary wastewater plumes. The overall oyster &delta15N gradient (16.0 / in Eastern Bay, 8.3 / in Lynnhaven River) decreased with flushing time, with increased salinity, and with increased shell height. Denitrification remains potentially confounding as it elevates nitrate &delta15N signals, potentially before oyster assimilation (via plankton). Nevertheless, oyster &delta15N is a powerful tool for indicating nitrogen sources across spatial and temporal scales.Item GRAZING AS A MANAGEMENT TOOL FOR CONTROLLING PHRAGMITES AUSTRALIS AND RESTORING NATIVE PLANT BIODIVERSITY IN WETLANDS(2010) Brundage, Jennifer Emilienne; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study examined the feasibility of grazing as a sustainable and low-impact means of controlling Phragmites. In addition, this study examined whether grazing of Phragmites by large herbivores (goats) in a wetland affects soil and soil water nutrient pools, and thus how grazing might affect nutrient export from the wetland. An isolated, created wetland at USDA's Beltsville Agricultural Research Center (BARC) in Beltsville, MD was divided into four grazed and four ungrazed plots. Two rounds of grazing significantly reduced Phragmites height, stem count, and biomass and increased some measures of plant diversity. Grazing significantly elevated soil water total nitrogen and total phosphorus levels and reduced soil water-soluble phosphorus levels. The nutrient pool analysis indicates that grazing reduced the fertility of the system. The results of this study will inform the development of an alternative, sustainable approach to controlling Phragmites that integrates the local agricultural community while benefiting the local ecology.Item Interregional differences in stream ecosystem responses to urbanization: causes and consequences(2010) Utz, Ryan Michael; Hilderbrand, Robert H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stream ecosystems are profoundly degraded by watershed urbanization. Hydrologic, geomorphic, chemical and thermal adjustment following urban development contributes to substantial biodiversity loss in impacted streams. However, the extent of degradation along an urban gradient may not be uniform among regions. The hydrogeologic and climatic setting in which a stream is located may influence the severity of abiotic and biotic impact induced by urban development. I explored and compared differences in stream ecosystem responses to urbanization between the Coastal Plain and Piedmont physiographic regions of the eastern United States. Taxon-specific responses of fishes and macroinvertebrates as well as the coherence of benthic invertebrate communities along gradients of landscape stressors were quantified. Hydrologic, chemical and thermal impact induced by watershed urbanization was compared between the two physiographic provinces using existent large datasets collected by various governmental entities. I also compared the severity geomorphic and sediment regime alteration in urban streams between regions using direct measurements of channel morphometry and in situ natural experiments within selected watersheds. Biotic sensitivity to urbanization was consistently found to be heightened in Piedmont streams relative to those in the Coastal Plain. Such trends were consistently observed for fish and macroinvertebrate taxa as well as for invertebrate community coherence. The most tolerant macroinvertebrate communities were associated with low channel slopes, effective soil permeability and high levels of wetland cover. Rural Coastal Plain streams exhibited fewer flood events that were longer in duration; however, flood hydrology was more impacted by urbanization in Coastal Plain streams relative to those of the Piedmont. Conversely, thermal impact induced by urbanization was greater in Piedmont streams. Experimental observations concluded that benthic sediment size structure, deposition and transport were more impacted by urban development in Piedmont streams relative to those of the Coastal Plain. My findings highlight interregional heterogeneity in stream ecosystem responses to landscape change, suggesting that effective watershed management decisions may need to consider the physiographic setting in order to improve efficacy. Furthermore, results suggest that watersheds characteristic of hydrogeomorphic attributes that effectively transfer water to channels during precipitation events may be acutely vulnerable to urban development.Item Interactions between an estuarine submersed plant bed and its physical and biogeochemical environment: Seasonal and spatial variation(2009) Gruber, Renee Kirstin; Kemp, William M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Annual cycles of growth and morphology were analyzed in a bed of the canopy-forming submersed aquatic vegetation (SAV) species, Stuckenia pectinata, in relation to seasonal water quality conditions in a Chesapeake Bay tributary. A rapid accumulation of aboveground plant material occurred during the spring period of high water clarity, which aided plants in circumventing light limitation during the summer period of low water clarity. During summer, this SAV bed strongly attenuated wave energy, which contributed to growth-promoting feedback effects that improved light and nutrient availability for plants. Modification of hydrodynamic conditions also resulted in several negative feedback effects on SAV growth. Feedbacks were regulated by plant stand size and density and seasonal changes in plant canopy architecture. The findings of this study illustrate the significant impacts SAV beds can have on their local environment, improving conditions and resulting in plant growth that could not otherwise occur in this degraded system.Item Organic nitrogen and carbon transformations in a stream network of Chesapeake Bay watershed(2009) Delaney, Katie M.; Kaushal, Sujay S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increased export of anthropogenically-derived nitrogen in streams has contributed to increased water quality problems. I investigated in-stream transformations of nitrogen and carbon at the benthic habitat and reach network scale. Both indicated large transformations of dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) along the Gwynns Falls urban stream network. In-stream transformation of DON and DOC declined from headwaters to outflow, with a mean 23% removal of DOC and 57% removal of DON. Transformation rates ranged from in-stream internal loading of 28 g/m2/day to in-stream removal of 740 g/m2/day for DOC (mean: uptake 64 g/m2/day) and in-stream internal loading of 4.8 g/m2/day to in-stream removal of 74 g/m2/day for DON (mean: uptake 3.5 g/m2/day). Urban stream networks may act as both "transporters" and "transformers" of nitrogen and knowledge regarding in-stream N transformations is critical in predicting the sources and removal of nitrogen en route to adjacent tidal waters.Item Predation by eastern mudminnows (Umbra pygmaea) on macroinvertebrates of temporary wetlands(2009) Lombardi, Susan Elizabeth; Lamp, William O.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fish play a substantial role in aquatic food webs, yet the effect of feeding activities of small stream fish that enter seasonally-flooded temporary wetlands during periods of hydrologic connectivity is not well understood. In this study, eastern mudminnows (Umbra pygmaea) were introduced to a fishless wetland in Caroline County, Maryland, and the aquatic macroinvertebrate community did not significantly change within two weeks. Gut contents of mudminnows collected from the wetland and a stream consisted primarily of dipteran larvae; ostracods were also a common food source for wetland mudminnows. Common prey not found in gut contents but present in the wetland were tested as food, and all taxa were consumed in a no-choice predation experiment. Mudminnows have the potential to directly affect multiple trophic levels and subsequent ecosystem functioning through predatory interactions with sustained hydrologic connectivity between fish sources and temporary wetlands.Item An RNA:DNA-based index of growth in juvenile Atlantic menhaden (Brevoortia tyrannus): laboratory calibration and field assessment(2009) Edwards, Jason Lee; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atlantic menhaden (Brevoortia tyrannus) is an ecologically and economically important species in the mid-Atlantic coastal ecosystem. Its population dynamics are influenced by growth and survival during juvenile occupancy in estuarine nursery habitats. Therefore, quantifying production of potential nursery areas is important to understanding population processes and defining essential fish habitat for this species. Based on laboratory growth experiments, an RNA:DNA-based growth model was developed for young-of-the-year menhaden. The temporal response of RNA:DNA to changes in feeding condition was also quantified in the laboratory. Results of these investigations indicate RNA:DNA as a reliable tool for estimating recent growth and condition in relation to habitat residency. RNA:DNA-based estimates of growth were combined with site-specific abundance estimates to evaluate the spatiotemporal variability in production of potential menhaden nursery habitats. Site-specific production estimates exhibited high spatiotemporal variability suggesting menhaden utilize a mosaic of habitats to promote production, rather than specific sites consistently generating high levels of production.Item PATTERNS OF WETLAND PLANT SPECIES RICHNESS ACROSS ESTUARINE RIVER GRADIENTS(2009) Sharpe, Peter James; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)It is widely accepted that in coastal wetlands a negative relationship exists between plant species richness (number of species) and salinity. However, the distribution of species richness across estuarine salinity gradients has not been closely examined. I hypothesized that plant species richness in coastal marshes (i.e., wetlands dominated by herbaceous plants) would follow a non-linear pattern with increased distance (salinity) downriver (Chapter 2). To test this hypothesis I conducted detailed marsh vegetation surveys along ≈ 50 km estuarine river gradients of the Nanticoke and Patuxent Rivers, MD/DE. I further hypothesized that the observed patterns of plant species richness on the Nanticoke and Patuxent Rivers could be accurately predicted by a mid-domain effect (MDE) model independent of measured abiotic factors using RangeModel 5.0 (Chapter 3). Lastly, I theorized that Marsh mesocosms subjected to intermediate salinity and inundation would exhibit significantly higher biomass and plant species richness compared to mesocosms subjected to extreme salt/fresh and flooding regimes utilizing a controlled greenhouse experiment (Chapter 4). I found that plant species richness can vary in both a linear (Patuxent River) and non-linear (Nanticoke River) pattern along an estuarine gradient. The MDE model did not explain a high proportion of the observed richness patterns for either river system compared to abiotic factors like porewater salinity. The controlled marsh mesocosm experiment supported the non-linear pattern of plant species richness observed along the Nanticoke River gradient, but did not show a significant difference in plant biomass or richness/diversity between purely fresh and low-salinity marsh mesocosms (α = 0.05). The results of this research suggest that tidal marsh plant richness/diversity patterns do not always conform to a simple linear relationship with increasing salinity and that the MDE is not as important of a mechanism in these communities compared to porewater salinity or flooding frequency. Furthermore tidal low salinity marshes exposed to elevated salinity and flooding frequencies are likely to see a shift in their plant community structure to more salt tolerant plants and less rich/diverse communities assuming they can accrete at a rate equal to or exceeding the present rates of sea-level rise in the Chesapeake Bay.